Java Hacks and Tricks for Prograramming

Here are the few java tricks and codes which will definitely help you to improve your programming skills.

import java.math.BigInteger;
import java.util.*;
public class Document {
public  static void main(String args[]) {
Scanner in = new Scanner(System.in);
String str = "Adarsh";
//replace substring in a String
String result = str.replaceFirst("ar", "A");
System.out.println(result);
//String upper case
System.out.println("String upperCase: " + str.toUpperCase());
//String lower case
System.out.println("String lowerCase: " + str.toLowerCase());
//length of string
System.out.println("Length: " + str.length());
//first index in string
System.out.println("First index of 'r': " + str.indexOf('r'));
//last index in string
System.out.println("Last index of 'a': " + str.lastIndexOf('a'));
//String difference
System.out.println("compare with 'Kumar': " + str.compareTo("Kumar"));
//String contains char sequence
System.out.println(str+" contain 'arsh': "+str.contains("arsh"));
//String to char Array
char charArray[] = str.toCharArray();
System.out.print("Char Array: ");
System.out.println(charArray);
//List to Array
List<String> list = Arrays.asList("C", "C++", "Java");
String[] array = list.toArray(new String[list.size()]);
System.out.println(Arrays.toString(array));
//ASCII
System.out.println("ASCII of numbers");
for(int i=48; i<57; i++){
System.out.print((char)i);
}
System.out.println();
System.out.println("ASCII of A-Z");
for(int i=65; i<91; i++){
System.out.print((char)i);
}
System.out.println();
System.out.println("ASCII of a-z");
for(int i=97; i<123; i++){
System.out.print((char)i);
}
System.out.println();
//character Input
System.out.println("Enter a Character");
char ch = in.next().charAt(0);
//Subtring
System.out.println("Substring of "+str+" 0 to 4 is: "+str.substring(1,4));
//String to Integer
String num = "100";
System.out.println("Integer form of '100': "+Integer.parseInt(num));
//Swapping of 2 numbers using XOR:
int a = 4, b=5;
System.out.println("Before Swapping a="+a+", b="+b);
a ^= b;
b ^= a;
a ^= b;
System.out.println("After Swapping a="+a+", b="+b);
//Multiply by 2
System.out.println("Multiply 3 with 2: "+ (3 << 1));
//Divide by 2
System.out.println("Divide 6 with 2: "+ (6 >> 1));
//Number of Digit
System.out.println((int)Math.floor(Math.log10(556)) +1);
//GCD using BigInteger
BigInteger b1 = BigInteger.valueOf(10);
BigInteger b2 = BigInteger.valueOf(5);
System.out.println("GCD of 10 & 5: "+b1.gcd(b2));
//Check Prime Number
System.out.println("Is 9 prime?: "+BigInteger.valueOf(9).isProbablePrime(1));
//Check if number is power of 2 or not
int x = 7;
System.out.println("Is "+x+" power of 2? "+(x!=0 && ((x&(x-1)) == 0)));
//sort array
int numArray[] = {1, 5, 3, 2, 4};
Arrays.sort(numArray);
for(Integer n: numArray){
System.out.print(n + " ");
}
System.out.println();
char ch2 = 'a';
//upper case character
ch2 = Character.toUpperCase(ch2);
System.out.println("Character upper case: "+ch2);
//lower case character
ch2 = Character.toLowerCase(ch2);
System.out.println("Lower upper case: "+ch2);
//List Sorting
List<Integer> numList= new ArrayList<>();
numList.add(5);
numList.add(1);
numList.add(3);
System.out.println("List Before Sorting");
for(Integer n: numList){
System.out.print(n+" ");
}
System.out.println();
Collections.sort(numList);
System.out.println("List After Sorting");
for(Integer n: numList){
System.out.print(n+" ");
}
System.out.println();
//Hash Map
HashMap<String, Integer> numHash = new HashMap<>();
numHash.put("A",65);
numHash.put("B",66);
numHash.put("C",67);
if(numHash.containsKey("A"))
System.out.println(numHash.get("A"));
if(numHash.containsValue(66))
System.out.println(numHash.get("B"));
System.out.println("Size Of HashMap: "+numHash.size());
numHash.remove("A");
System.out.println("Size Of HashMap after removing First Object: "+numHash.size());
numHash.replace("C",0);
System.out.println(numHash.get("C"));
numHash.clear();
if(numHash.isEmpty())
System.out.println("HashMap is Empty");
//Stack
Stack<Integer> stack = new Stack<>();
stack.push(2);
stack.push(3);
stack.push(4);
System.out.println("Top Element in Stack: "+stack.peek());
System.out.println("Popping Top Element in Stack: "+stack.pop());
System.out.println("Top Element in Stack: "+stack.peek());
stack.clear();
if (stack.isEmpty())
System.out.println("Stack is Empty");
}
}

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

import java.math.BigInteger;

import java.util.*;

public class Document {

public static void main(String args[]) {

Scanner in = new Scanner(System.in);

String str = "Adarsh";

//replace substring in a String

String result = str.replaceFirst("ar", "A");

System.out.println(result);

//String upper case

System.out.println("String upperCase: " + str.toUpperCase());

//String lower case

System.out.println("String lowerCase: " + str.toLowerCase());

//length of string

System.out.println("Length: " + str.length());

//first index in string

System.out.println("First index of 'r': " + str.indexOf('r'));

//last index in string

System.out.println("Last index of 'a': " + str.lastIndexOf('a'));

//String difference

System.out.println("compare with 'Kumar': " + str.compareTo("Kumar"));

//String contains char sequence

System.out.println(str+" contain 'arsh': "+str.contains("arsh"));

//String to char Array

char charArray[] = str.toCharArray();

System.out.print("Char Array: ");

System.out.println(charArray);

//List to Array

List<String> list = Arrays.asList("C", "C++", "Java");

String[] array = list.toArray(new String[list.size()]);

System.out.println(Arrays.toString(array));

//ASCII

System.out.println("ASCII of numbers");

for(int i=48; i<57; i++){

System.out.print((char)i);

}

System.out.println();

System.out.println("ASCII of A-Z");

for(int i=65; i<91; i++){

System.out.print((char)i);

}

System.out.println();

System.out.println("ASCII of a-z");

for(int i=97; i<123; i++){

System.out.print((char)i);

}

System.out.println();

//character Input

System.out.println("Enter a Character");

char ch = in.next().charAt(0);

//Subtring

System.out.println("Substring of "+str+" 0 to 4 is: "+str.substring(1,4));

//String to Integer

String num = "100";

System.out.println("Integer form of '100': "+Integer.parseInt(num));

//Swapping of 2 numbers using XOR:

int a = 4, b=5;

System.out.println("Before Swapping a="+a+", b="+b);

a ^= b;

b ^= a;

a ^= b;

System.out.println("After Swapping a="+a+", b="+b);

//Multiply by 2

System.out.println("Multiply 3 with 2: "+ (3 << 1));

//Divide by 2

System.out.println("Divide 6 with 2: "+ (6 >> 1));

//Number of Digit

System.out.println((int)Math.floor(Math.log10(556)) +1);

//GCD using BigInteger

BigInteger b1 = BigInteger.valueOf(10);

BigInteger b2 = BigInteger.valueOf(5);

System.out.println("GCD of 10 & 5: "+b1.gcd(b2));

//Check Prime Number

System.out.println("Is 9 prime?: "+BigInteger.valueOf(9).isProbablePrime(1));

//Check if number is power of 2 or not

int x = 7;

System.out.println("Is "+x+" power of 2? "+(x!=0 && ((x&(x-1)) == 0)));

//sort array

int numArray[] = {1, 5, 3, 2, 4};

Arrays.sort(numArray);

for(Integer n: numArray){

System.out.print(n + " ");

}

System.out.println();

char ch2 = 'a';

//upper case character

ch2 = Character.toUpperCase(ch2);

System.out.println("Character upper case: "+ch2);

//lower case character

ch2 = Character.toLowerCase(ch2);

System.out.println("Lower upper case: "+ch2);

//List Sorting

List<Integer> numList= new ArrayList<>();

numList.add(5);

numList.add(1);

numList.add(3);

System.out.println("List Before Sorting");

for(Integer n: numList){

System.out.print(n+" ");

}

System.out.println();

Collections.sort(numList);

System.out.println("List After Sorting");

for(Integer n: numList){

System.out.print(n+" ");

}

System.out.println();

//Hash Map

HashMap<String, Integer> numHash = new HashMap<>();

numHash.put("A",65);

numHash.put("B",66);

numHash.put("C",67);

if(numHash.containsKey("A"))

System.out.println(numHash.get("A"));

if(numHash.containsValue(66))

System.out.println(numHash.get("B"));

System.out.println("Size Of HashMap: "+numHash.size());

numHash.remove("A");

System.out.println("Size Of HashMap after removing First Object: "+numHash.size());

numHash.replace("C",0);

System.out.println(numHash.get("C"));

numHash.clear();

if(numHash.isEmpty())

System.out.println("HashMap is Empty");

//Stack

Stack<Integer> stack = new Stack<>();

stack.push(2);

stack.push(3);

stack.push(4);

System.out.println("Top Element in Stack: "+stack.peek());

System.out.println("Popping Top Element in Stack: "+stack.pop());

System.out.println("Top Element in Stack: "+stack.peek());

stack.clear();

if (stack.isEmpty())

System.out.println("Stack is Empty");

}

Output

AdAsh
String upperCase: ADARSH
String lowerCase: adarsh
Length: 6
First index of 'r': 3
Last index of 'a': 2
compare with 'Kumar': -10
Adarsh contain 'arsh': true
Char Array: Adarsh
[C, C++, Java]
ASCII of numbers
012345678
ASCII of A-Z
ABCDEFGHIJKLMNOPQRSTUVWXYZ
ASCII of a-z
abcdefghijklmnopqrstuvwxyz
Enter a Character
p
Substring of Adarsh 0 to 4 is: dar
Integer form of '100': 100
Before Swapping a=4, b=5
After Swapping a=5, b=4
Multiply 3 with 2: 6
Divide 6 with 2: 3
3
GCD of 10 & 5: 5
Is 9 prime?: false
Is 7 power of 2? false
1 2 3 4 5 
Character upper case: A
Lower upper case: a
List Before Sorting
5 1 3 
List After Sorting
1 3 5 
65
66
Size Of HashMap: 3
Size Of HashMap after removing First Object: 2
0
HashMap is Empty
Top Element in Stack: 4
Popping Top Element in Stack: 4
Top Element in Stack: 3
Stack is Empty

AdAsh

String upperCase: ADARSH

String lowerCase: adarsh

Length: 6

First index of 'r': 3

Last index of 'a': 2

compare with 'Kumar': -10

Adarsh contain 'arsh': true

Char Array: Adarsh

[C, C++, Java]

ASCII of numbers

012345678

ASCII of A-Z

ABCDEFGHIJKLMNOPQRSTUVWXYZ

ASCII of a-z

abcdefghijklmnopqrstuvwxyz

Enter a Character

Substring of Adarsh 0 to 4 is: dar

Integer form of '100': 100

Before Swapping a=4, b=5

After Swapping a=5, b=4

Multiply 3 with 2: 6

Divide 6 with 2: 3

GCD of 10 & 5: 5

Is 9 prime?: false

Is 7 power of 2? false

1 2 3 4 5

Character upper case: A

Lower upper case: a

List Before Sorting

5 1 3

List After Sorting

1 3 5

Size Of HashMap: 3

Size Of HashMap after removing First Object: 2

HashMap is Empty

Top Element in Stack: 4

Popping Top Element in Stack: 4

Top Element in Stack: 3

Stack is Empty